The present invention relates to a process for fabricating soft magnetic thin films which are primarily applied to various magnetic heads including an induction type magnetic head, a magnetoresistance type magnetic head (MR head), and an MR induction type composite head having an induction head portion and an MR head portion.
In recent years, magnetic recording of much higher density than ever before has been put forward. With this, thin film magnetic heads using soft magnetic thin films as magnetic poles, and reproducing MR heads making use of magnetoresistance effect have been under remarkable developments.
An MR head is designed to read external magnetic signals through a resistance change in a reading sensor formed of magnetic material. A characteristic feature of the MR head is that high outputs are achievable even when magnetic recording is performed at high linear densities because outputs are not dependent on its relative speed with respect to a recording medium. To increase resolving power and obtain good-enough properties at high frequencies, the MR head is usually constructed by sandwiching a magnetoresistance film (an MR film) between a pair of magnetic shielding films (a shielded MR head).
For the MR head that is a reproducing head, an MR induction type composite head is used, in which an MR head portion is provided in the form of an integral piece of an induction type head portion for recording purposes.
For magnetic shielding films or magnetic poles in the MR heads or the MR induction type composite heads, it is preferable to use thin films excellent in soft magnetic properties. Fe--Zr--N base soft magnetic thin films set forth in JP-B 7-60767 and JP-A 3-1513, for instance, are available to this end.
MR films are generally of low heat resistance. In particular, multilayer films having giant magnetoresistance (GMR) effect (artificial lattice films composed of a laminate of thin films each having a thickness of about 5 nm) are likely to undergo considerable degradation because mutual dispersion occurs between thin films upon heated. It is thus required that annealing for the purpose of improving the soft magnetic properties of magnetic shielding films or magnetic poles be done at temperatures below 300.degree. C.
In the case of metal nitride thin films such as the aforesaid Fe--Zr--N base thin films, however, stress relieving cannot be achieved unless they are thermally treated at a temperature of at least 300.degree. C. This is because their compressive stresses are increased by the penetration of the light element N between metallic lattices. In the publications mentioned above, it is at an annealing temperature greater than 350.degree. C. when practical soft magnetic properties are obtainable, although such publications make no reference to film stresses. Generally speaking, a problem with a thin film, of which compressive stress is not fully relieved, is that when applied to a relatively thick portion such as a magnetic pole in the induction type head portion or a magnetic shielding film in the MR head portion, it is often delaminated from an underlaid insulating layer, or otherwise other films peel off. Another problem is that it is difficult to obtain satisfactory soft magnetic properties due to the influence of magnetostriction.
A soft magnetic thin film, when it is actually applied to a magnetic pole or magnetic shield in a magnetic head, is not only strongly affected by the stress of an underlaid insulating layer, etc., but also affected by the stresses of upper layers that are formed on the soft magnetic thin film. It follows that even if the soft magnetic thin film has reduced stress in itself, it is not always possible to prevent it from peeling off or better its soft magnetic properties.
When forming a soft magnetic thin film that is applied to a magnetic head having an MR head portion and so should be thermally treated at a temperature below 300.degree. C., therefore, it is required to control forming conditions so as to impart the optimum stress to it depending on layers formed under or over it, thereby preventing its delamination from the underlaid layer and achieving good-enough soft magnetic properties.
Thus, it is an object of the present invention to provide a process for fabricating a soft magnetic thin film that is applied to a magnetic shielding film or magnetic pole in an MR head or an MR induction type composite head including a reproducing MR head portion and a recording induction head portion, wherein said soft magnetic thin film can be stress controlled without applying any high-temperature annealing thereto.